1. Field of the Invention
The present invention relates to a driving mechanism that rotationally drives a shaft member, and to an image forming apparatus including the driving mechanism.
2. Related Art
Conventionally, there exist types of an image forming apparatus such as a printer or copying machine, which have a photosensitive drum as an image carrier. The photosensitive drum includes a photosensitive drum main body and a shaft member. The shaft member is disposed in a rotation center of the photosensitive drum main body so as to penetrate the photosensitive drum main body. The photosensitive drum is rotationally driven as a result of a rotational driving force being directly or indirectly transmitted from a rotational driving unit to the shaft member.
A known example of a driving mechanism that rotationally drives a photosensitive drum is a driving mechanism that is provided with a metallic transmission belt that is stretched over an output shaft of a motor and a shaft member of a photosensitive drum via a pulley, in a state in which the output shaft of the motor is disposed so as to be parallel with the shaft member of the photosensitive drum. Such a driving mechanism transmits a rotational driving force of the motor to the shaft member of the photosensitive drum by the metallic transmission belt.
In an image forming apparatus including a driving mechanism such as described above, one end of the output shaft of the motor is rotatably supported by a motor main body. Moreover, the transmission belt is stretched over the other end of the output shaft of the motor via the pulley. In such an image forming apparatus, the metallic transmission belt is stretched over the output shaft of the motor and the shaft member of the photosensitive drum via the pulley in a state of having a predetermined tensile force, so as not to slip with respect to the output shaft of the motor, the shaft member of the photosensitive drum, the pulley thus interposed, etc. As a result, the metallic transmission belt suppresses micro-vibration or the like caused by engagement of gears as compared with a case in which a rotational driving force is transmitted via gears. Therefore, the metallic transmission belt can stably transmit a rotational driving force from the motor to the shaft member of the photosensitive drum.
Incidentally, there are many cases in which an output shaft of a motor used for a small-sized device such as an image forming apparatus has a small diameter. Therefore, there are cases in which the output shaft of the motor may be flexurally deformed toward the shaft member side of the photosensitive drum, due to a tensile force of the metallic transmission belt that is stretched over the output shaft and the shaft member of the photosensitive drum.